This invention relates to the reduction of glare, or unwanted specularly reflected light, in flash photography. Because flash photography uses a small, very bright, light source, rather than the diffuse light of ordinary ambient illumination, and moreover, because in self-contained flash cameras this source of light shines directly, or face-on to the illuminated scene, there are often unwanted bright reflections or highlights in the resulting photograph. These include specular reflections off of glass, metal surfaces, and the shiny surface of skin, often on the faces of the subjects of the photograph.
Van Der Meer in U.S. Pat. No. 3,709,119 describes a close-up (e.g., 13-17 inches) photographic system utilizing a flash unit for illumination, and light polarizing means for reducing reflected glare. The polarizers used in the system are absorptive sheet polarizers of the type manufactured by Polaroid Corporation (Cambridge, Mass.) that function by absorbing very effectively one linear polarization of light and transmitting a portion of the second linear polarization of light from an unpolarized light source. The light transmitted by such absorptive polarizing filters can be highly polarized, but only about 30% to 40% of the initially unpolarized light is transmitted.
Grinberg et al. in U.S. Pat. No. 4,073,571, and Barnik et al. in U.S. Pat. No. 5,295,009 describe light sources incorporating reflective sheet circular polarizers, based on cholesteric liquid crystal materials. Such reflective sheet circular polarizers are currently being developed for commercial use in the polarized backlight illumination of the liquid crystal display panels in portable computers. The 3M company (St. Paul, Minn.) manufactures reflective sheet linear polarizers based on multilayer polymer materials, under the product name Dual Brightness Enhancement Film (DBEF). These polarizers are currently used in the polarized back-light illumination of liquid crystal displays in portable computers.
The information described above is not admitted to be prior art to the present invention, but is provided only to assist the understanding of the reader.